Precursors and methods for atomic layer deposition of transition metal oxides

ABSTRACT

Methods are provided herein for forming transition metal oxide thin films, preferably Group IVB metal oxide thin films, by atomic layer deposition. The metal oxide thin films can be deposited at high temperatures using metalorganic reactants. Metalorganic reactants comprising two ligands, at least one of which is a cycloheptatriene or cycloheptatrienyl (CHT) ligand are used in some embodiments. The metal oxide thin films can be used, for example, as dielectric oxides in transistors, flash devices, capacitors, integrated circuits, and other semiconductor applications.

REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional applicationNo. 61/308,263, filed Feb. 25, 2010. The priority application is herebyincorporated by reference in its entirety.

PARTIES OF JOINT RESEARCH AGREEMENT

The invention claimed herein was made by, or on behalf of, and/or inconnection with a joint research agreement between the University ofHelsinki and ASM Microchemistry Oy signed on Nov. 14, 2003 and renewedin 2008. The agreement was in effect on and before the date the claimedinvention was made, and the claimed invention was made as a result ofactivities undertaken within the scope of the agreement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates generally to methods and compositionsfor depositing transition metal oxide thin films, such as titanium,zirconium and hafnium oxide thin films, by atomic layer deposition usingmetalorganic precursors. The metalorganic precursors comprise at leastone cycloheptatriene (CHT) ligand.

2. Description of the Related Art

Atomic layer deposition (ALD) is a self-limiting process, wherebyalternated pulses of reactants saturate a substrate surface. Thedeposition conditions and precursors are selected such that an adsorbedlayer of precursor in one pulse leaves a surface termination that isnon-reactive with the gas phase reactants of the same pulse. Asubsequent pulse of different reactants reacts with the previoustermination to enable continued deposition. Thus, each cycle ofalternated pulses typically leaves no more than about one molecularlayer of the desired material. The principles of ALD type processes havebeen presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3,Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, thedisclosure of which is incorporated herein by reference. Variations ofALD have been proposed that allow for modulation of the growth rate.However, to provide for high conformality and thickness uniformity,these reactions are still more or less self-saturating.

While ALD processes can be used to deposit films at lower temperatures,typically CVD processes have been used for higher temperature growthbecause the reactions occur more rapidly at higher temperatures. Inaddition, some ALD processes can lose their self limiting nature at hightemperatures. In some cases, higher temperatures can cause undesirabledecomposition of some precursors. Some precursor decomposition candisrupt the self limiting nature of the ALD process, for example if theproducts of the decomposition reaction react with each other and/orreact with the adsorbed species to deposit material on the substratesurface.

Atomic layer deposition (ALD) of Group IVB metal oxides, such asTiO_(x), ZrO₂ and HfO₂, has been studied for years. However, highertemperature ALD options for these metal oxides are quite limited. Metalhalide reactants are typically used; however, metal halides areincompatible with some materials and processes. Some metal-organicprecursors have also been used. However, these reactants have not beenwell suited for higher temperature deposition processes.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, methods forforming transition metal oxide thin films on a substrate in a reactionchamber by atomic layer deposition using metalorganic reactants areprovided. Organometallic reactants are used in some embodiments. In someembodiments the transition metal oxide thin films are Group IVB metaloxide thin films. In some embodiments, the methods comprise providing avapor phase pulse of a first reactant comprising a first Group IVBmetalorganic precursor to a reaction chamber such that it forms no morethan a monolayer on a substrate in the reaction chamber; removing excessfirst reactant from the reaction chamber; providing a vapor phase pulseof a second reactant comprising oxygen to the reaction chamber such thatit converts the adsorbed Group IVB metal reactant to a metal oxide; andremoving excess second reactant and any reaction byproducts from thereaction chamber. The providing and removing steps are repeated until athin metal oxide film of a desired thickness and composition isobtained. The substrate temperature during the providing and removingsteps may be above about 300° C., more preferably above about 350° C. Insome embodiments the metalorganic precursor is an organometallicprecursor, comprising a carbon-metal bond.

In accordance with another aspect of the present invention, methods forforming transition metal oxide films, preferably Group IVB metal oxidefilms, by atomic layer deposition comprise alternately and sequentiallycontacting a substrate with vapor phase pulses of a cycloheptatrienyl orcycloheptatriene (CHT) metal reactant and an oxygen source. Thealternate and sequential pulses are repeated until a thin film of adesired thickness is obtained.

CHT metal reactants are metalorganic, typically organometalliccompounds, comprising at least one chycloheptatrienyl orcycloheptatriene ligand (a CHT ligand). In some embodiments the CHTmetal reactant comprises only two ligands, including at least onecycloheptatrienyl or cycloheptatriene (CHT) ligand. In some embodimentsthe CHT metal reactant comprises two CHT ligands. In some embodimentsthe CHT metal reactant comprises two cycloheptatrienyl ligands. In otherembodiments the CHT metal reactant comprises one CHT ligand and onecyclopentadienyl ligand (Cp). In some embodiments, the CHT reactant doesnot comprise a halide. In some embodiments, the CHT reactant comprisesone cycloheptadienyl (CHD) ligand. In some embodiments, the CHT reactantcomprises two C₇H₈ cycloheptatriene ligands.

In some embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (I) R_(x)Cp-M-CHT, where R_(x)Cp represents substituted or        unsubstituted cyclopentadienyl, CHT is cycloheptatrienyl (C₇H₇)        and M is selected from Ti, Zr and Hf.

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (II) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-Cp(R₈R₉R₁₀R₁₁R₁₂), where M is        selected from Ti, Zr and Hf, R₁₋₁₂ can independently be H or an        alkyl group.

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (III) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHT(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄), where M is        selected from Ti, Zr and Hf, R₁₋₁₄ can independently be H or an        alkyl group.

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (IV) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-L, where M is selected from Ti, Zr        and Hf, R₁₋₇ can independently be H or an alkyl group and L is a        mono or bidentate alkyl, cycloalkyl, alkoxy, amide or imido        group. L may also be a acyclic or cyclic dienyl ligand.

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (V) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHD(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where        M is selected from Ti, Zr and Hf, R₁₋₁₆ can independently be H        or an alkyl group and CHD is a cyloheptadienyl (C₇H₉).

In other embodiments a CHT reactant it is selected from the groupconsisting of reactants of the formula:

-   -   (VI) (R₁R₂R₃R₄R₅R₆R₇R₈)X-M-X(R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where M        is selected from Ti, Zr and Hf, R₁₋₁₄ can independently be H or        an alkyl group and X is cycloheptariene (C₇H₈).

In some embodiments, a CHT metal reactant can take different formsdepending on the conditions. For example, in some embodiments a CHTmetal reactant may have formula (V) under some conditions, but may be inthe form of formula (VI) under other conditions.

In the formulas (I)-(VI) CHT, CHD or X, denote the structure of theligand i.e. C₇ ring structure with double bonds or delocalizedelectrons, where different groups R₁-R₁₆ can attach. For example,according to formula (IV) the compound can be C₇H₇-M-L or((CH₃)₃C₇H₄)-M-L, not H₇C₇H₇-M-L or (H₄(CH₃)₃C₇H₇)-M-L, respectively.

In another aspect of the invention, transition metal nitride thin films,such as Group IVB metal nitride films, are deposited by ALD using atransition metal CHT reactant and a nitrogen containing reactant. Insome embodiments the metal CHT reactant comprises two CHT ligands. Insome embodiments the CHT reactant does not comprise a Cp group. In someembodiments, the CHT reactant comprises two C₇H₈ cycloheptatrieneligands.

In still another aspect of the invention, transition metal carbide thinfilms, such as Group IVB metal carbide films, are deposited by ALD usinga metal CHT reactant. In some embodiments the metal CHT reactantcomprises two CHT ligands. In some embodiments, the CHT reactant doescomprise two C₇H₈ cycloheptatriene ligands.

In another aspect of the invention, methods of synthesizing transitionmetal precursors comprising one or more CHT ligands are provided. Insome embodiments, methods of synthesizing (C₇H₈)M(C₇H₈), where M is atransition metal, preferably a Group IVB metal, are provided. Themethods may comprise forming a reaction mixture by combining atransition metal reactant with ferric chloride, cycloheptatriene andtetrahydrofuran (THF) in a flask containing magnesium chips. Thetransition metal reactant may be, for example, a Group IVB transitionmetal reactant, preferably a metal halide. Exemplary reactants includetransition metal chlorides. In one embodiment, the transition metalreactant is TiCl₄.

These and other embodiments will become readily apparent to thoseskilled in the art from the following detailed description, theinvention not being limited to any particular preferred embodimentsdisclosed.

Certain objects and advantages of the disclosed precursors and methodshave been described herein. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment. Thus, for example, those skilled in theart will recognize that the invention may be embodied or carried out ina manner that achieves or optimizes one advantage or group of advantagesas taught herein without necessarily achieving other objects oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of CpTiCHT (left) and (MeCp)ZrCHT (right).

FIG. 2 shows the TGA curves measured for CpTiCHT and (MeCp)ZrCHT.

FIG. 3 is a graph of growth rate at various temperatures (top) and agraph of saturation as measured by growth rate for different metalreactant pulse lengths (bottom).

FIG. 4 shows TofERDA data for ZrO₂ films deposited using (MeCp)ZrCHT andO₃ at various temperatures.

FIGS. 5 a, 5 b and 5c show XRD data for ZrO₂ films deposited using(MeCp)ZrCHT and O₃ at various temperatures.

FIG. 6 represents graphs of GIXRD data for ZrO₂ films deposited using(MeCp)ZrCHT and O₃.

FIG. 7 illustrates experiments to characterize the electrical propertiesof ZrO₂ films deposited using (MeCp)ZrCHT and O₃.

FIG. 8 is a flow chart of an embodiment of an ALD process for depositinga Group IVB metal oxide using a CHT metal precursor.

FIG. 9 is a schematic of the crystal structure of Ti(C₇H₈)₂. Theformulation may also be (C₇H₇)Ti(C₇H₉) i.e. (CHT)Ti(CHD).

FIG. 10 shows TG, DTG and SDTA curves measured for (CHT)Ti(CHD).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Methods and compositions for forming transition metal oxide films usingmetalorganic precursors are described herein. While primarilyillustrated in the context of forming Group IVB metal oxide films, othertransition metals can be substituted for the Group IVB metals in someembodiments, as will be recognized by the skilled artisan. In addition,although the thin films are generally described with respect to theformation of an integrated circuit, such as a capacitor or transistor,the skilled artisan will readily appreciate the application of theprinciples and advantages disclosed herein to various contexts in whichmetal oxide thin films are useful. For example, transparent titaniumoxide films can be used in flat panel displays, LEDs, and solar cells.

In addition, although illustrated primarily in terms of deposition oftransition metal oxide thin films, in some embodiments transition metalnitride or metal carbide films, such as Group IVB metal nitride andcarbide films, can be deposited by ALD using the disclosed metalprecursors.

As used herein, the term metal oxide film refers to a transition metaloxide film unless otherwise stated. Preferred transition metal oxidefilms are Group IVB metal oxide films. Group IVB metal oxide thin filmsinclude oxide films comprising titanium (Ti), zirconium (Zr) and/orhafnium (Hf). Exemplary Group IVB metal oxide films that arespecifically discussed herein include TiO₂, ZrO₂ and HfO₂. Other GroupIVB metal oxide films will be apparent to the skilled artisan. Inaddition, as noted above, in some embodiments the Group IVB metals canbe substituted with other transition metals, as will be understood bythe skilled artisan.

In some embodiments, transition metal oxide films are deposited on asubstrate by atomic layer deposition (ALD) type processes utilizing oneor more metalorganic precursors. In some embodiments the metalorganicprecursor is an organometallic precursor and thus comprises acarbon-metal bond. As discussed below, in some embodiments depositiontemperatures of greater than 300° C. are used. In other embodiments,deposition temperatures of greater than 350° C. are used.

In particular embodiments, CHT metal reactants are utilized. CHT metalreactants are metal reactants comprising at least one CHT ligand. TheCHT metal reactant may be a metalorganic compound and in someembodiments is an organometallic compound. CHT ligands arecycloheptatrienyl and cycloheptatriene ligands. Thus, CHT metalreactants comprise at least one cycloheptatrienyl ligand or, in somecases, at least one cycloheptatriene ligand. The CHT metal reactantsused herein typically comprise only two ligands, one of which is a CHTligand (cycloheptatrienyl or cycloheptatriene). In some embodiments, thereactants comprise either two CHT ligands or one CHT ligand and onecyclopentadienyl (Cp) ligand. In some embodiments the CHT reactantcomprises two cycloheptatrienyl ligands. In some embodiments, the CHTreactant comprises two C₇H₈ cycloheptatriene ligands. In otherembodiments the CHT metal reactants comprise one CHT ligand and anotherligand such as a mono or bidentate alkyl, cycloalkyl, alkoxy, amide orimido group. In other embodiments the CHT metal reactants comprise oneCHT ligand and another ligand such as a dienyl ligand. In someembodiments the CHT metal reactant comprises a transition metal.However, the CHT metal reactants typically comprise one or more GroupIVB metals. In some embodiments, the CHT reactants do not comprise ahalide.

In some embodiments, CHT metal reactants have the general formula:

-   -   (I) RxCp-M-CHT, where RxCp represents substituted or        unsubstituted cyclopentadienyl, CHT is cycloheptatrienyl (C₇H₇)        and M is selected from Ti, Zr and Hf.

In other embodiments, CHT metal reactants have the general formula:

-   -   (II) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-Cp(R₈R₉R₁₀R₁₁R₁₂), where M is        selected from Ti, Zr and Hf, R₁₋₁₂ can independently be H or an        alkyl group, and may be a bridged or substituted alkyl.        Exemplary alkyl groups include, but are not limited to Me, Et,        Pr, ^(i)Pr, Bu, ^(t)Bu and other C₁-C₁₀ alkyls. Other alkyl        groups that may be used will be apparent to the skilled artisan.

In still other embodiments, the CHT metal reactants have the generalformula:

-   -   (III) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHT(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄), where M is        selected from Ti, Zr and Hf, R₁₋₁₄ can independently be H or an        alkyl group, and may be a bridged or substituted alkyl.        Exemplary alkyl groups include, but are not limited to Me, Et,        Pr, ^(i)Pr, Bu, ^(t)Bu and other C₁-C₁₀ alkyls. Other alkyl        groups that may be used will be apparent to the skilled artisan.

In still other embodiments, the CHT metal reactants have the generalformula:

-   -   (IV) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-L, where M is selected from Ti, Zr        and Hf; R₁₋₇ can independently be H or an alkyl group, and may        be a bridged or substituted alkyl; and L is either a mono or        bidentate alkyl, cycloalkyl, alkoxy, amide or imido group. L may        also be a acyclic or cyclic dienyl ligand. Exemplary alkyl        groups include, but are not limited to Me, Et, Pr, ^(i)Pr, Bu,        ^(t)Bu and other C₁-C₁₀ alkyls. Other alkyl groups that may be        used will be apparent to the skilled artisan. Exemplary alkoxy        groups include OMe, OEt, O^(i)Pr, O^(t)Bu, O₂CMe and O₂C^(t)Bu.        Exemplary amide groups include N(Me)₂, N(MeEt) and N(Et)₂.        Exemplary dienyl ligands include 2,4-dimethylpenta-1,4-dienyl        and hepta-2,5-dienyl.

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (V) (R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHD(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where        M is selected from Ti, Zr and Hf; R₁₋₁₆ can independently be H        or an alkyl group, and may be a bridged or substituted alkyl.        Exemplary alkyl groups include, but are not limited to Me, Et,        Pr, ^(i)Pr, Bu, ^(t)Bu and other C₁-C₁₀ alkyls. Other alkyl        groups that may be used will be apparent to the skilled artisan.        CHD is a cyloheptadiene (C₇H₉).

In other embodiments, a CHT metal reactant is selected from the groupconsisting of reactants of the formula:

-   -   (VI) (R₁R₂R₃R₄R₅R₆R₇R₈)X-M-X(R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where M        is selected from Ti, Zr and Hf; R₁₋₁₆ can independently be H or        an alkyl group, and may be a bridged or substituted alkyl.        Exemplary alkyl groups include, but are not limited to Me, Et,        Pr, ^(i)Pr, Bu, ^(t)Bu and other C₁-C₁₀ alkyls. Other alkyl        groups that may be used will be apparent to the skilled artisan.        X is cycloheptatriene (C₇H₈).

In some embodiments, a CHT metal reactant can take different formsdepending on the conditions. For example, in some embodiments a CHTmetal reactant may have formula (V) under some conditions, but may be inthe form of formula (VI) under other conditions.

In the formulas (I)-(VI) CHT, CHD or X, denote the structure of ligandi.e. C₇ ring structure with double bonds or delocalized electrons, wheredifferent groups R₁-R₁₆ can attach. For example, according to formula(IV) the compound can be C₇H₇-M-L or ((CH₃)₃C₇H₄)-M-L, not H₇C₇H₇-M-L or(H₄(CH₃)₃C₇H₇)-M-L, respectively.

In some embodiments one or more of the alkyl groups in R₁-R₁₆ mentionedin formulas (I)-(VI) may be C₁-C₂ alkyls, such as Me or Et, while inother embodiments one or more of the alkyl groups in R₁-R₁₆ mentioned informulas (I)-(VI) may be C₃-C₁₀ alkyls, such as Pr, ^(i)Pr, Bu and^(t)Bu.

In some embodiments one or more of the R₁-R₁₄ substituents mentioned informulas (I)-(VI) are other than hydrogen. In yet other embodiments twoor more of the R₁-R₁₄ substituents mentioned in formulas (I)-(VI) areother than hydrogen. In yet other embodiments three or more of theR₁-R₁₆ substituents mentioned in formulas (I)-(VI) are other thanhydrogen.

FIG. 1 illustrates the structures of two exemplary reactants, CpTiCHTand (MeCp)ZrCHT.

Atomic Layer Deposition Processes

ALD processes are generally based on controlled, self-limiting surfacereactions of precursor chemicals. Gas phase reactions are avoided byfeeding the precursors alternately and sequentially into the reactionchamber. Vapor phase reactants are separated from each other in thereaction chamber, for example, by removing excess reactants and/orreactant byproducts from the reaction chamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure.Deposition temperatures are typically maintained below the thermaldecomposition temperature of the reactants but at a high enough level toavoid condensation of reactants and to provide the activation energy forthe desired surface reactions. However, in some embodiments some minordecomposition may take place without significantly disrupting the stepcoverage and uniformity of the ALD process. Of course, the appropriatetemperature window for any given ALD reaction will depend upon a varietyof factors, including without limitation the surface termination and theparticular reactant species involved.

In some embodiments, thin films are deposited at deposition temperaturesof about 100 to about 500° C., more preferably about 150 to about 400°C. and in some embodiments about 300 to about 400° C. Particulardeposition temperatures for some specific embodiments are providedbelow.

In some embodiments, metal oxide films are deposited on a substrate byatomic layer deposition (ALD) type processes utilizing one or moremetalorganic precursors at temperatures greater than about 300° C. or attemperatures greater than about 350° C. In some of these embodiments,the metalorganic precursors are organometallic precursors. In someembodiments the precursors are metal CHT precursors as described herein.

A first transition metal reactant is conducted or pulsed into thechamber in the form of vapor phase pulse and contacted with the surfaceof the substrate. Conditions are preferably selected such that no morethan about one monolayer of the first reactant is adsorbed on thesubstrate surface in a self-limiting manner. Excess first reactant andreaction byproducts, if any, are removed from the reaction chamber, suchas by purging with an inert gas. The appropriate pulsing and purgingtimes can be readily determined by the skilled artisan based on theparticular circumstances.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, more preferably betweenabout 0.5 and 10, and still more preferably between about 1 and 5seconds. However, other purge times can be utilized if necessary, suchas where highly conformal step coverage over extremely high aspect ratiostructures or other structures with complex surface morphology isneeded. Also, batch ALD reactors can utilize longer purging timesbecause of increased volume and surface area.

A second gaseous reactant is pulsed into the chamber where it reactswith the first reactant bound to the surface. Excess second reactant andgaseous byproducts of the surface reaction are removed from the reactionchamber, preferably by purging with the aid of an inert gas and/orevacuation. The steps of pulsing and purging are repeated until a thinfilm of the desired thickness has been formed on the substrate, witheach cycle leaving typically less than or no more than a molecularmonolayer. The second reactant may be, for example, an oxygen containingreactant, such that a metal oxide is formed. In other embodiments thesecond reactant may comprise nitrogen or carbon, in order to form metalnitrides or metal carbides, respectively.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactants is supplied in each phase tosaturate the susceptible structure surfaces. Surface saturation ensuresreactant occupation of all available reactive sites (subject, forexample, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. However, in some embodiments, someminor non-self-limiting deposition may occur which does notsignificantly disturb the unique properties of ALD process.

According to some embodiments, a transition metal oxide thin film,preferably a Group IVB metal oxide thin film, is formed on a substrateby an ALD type process comprising multiple metal oxide depositioncycles, each metal oxide deposition cycle comprising:

providing a first vapor phase reactant pulse comprising a firstmetalorganic reactant to the reaction chamber such that it forms no morethan a monolayer on the substrate,

wherein the metalorganic reactant comprises a transition metal,preferably a Group IVB metal;

removing excess first reactant from the reaction chamber;

providing a second vapor phase reactant pulse comprising a secondreactant to the reaction chamber, wherein the second reactant comprisesoxygen; and removing excess second reactant and any reaction byproductsfrom the reaction chamber.

The providing and removing steps are repeated until a thin film of adesired thickness and composition is obtained. In some embodiments, thedeposition cycle is carried out at a temperature of at least 300° C. oreven at least 350° C.

Further, in some embodiments the metalorganic reactant is anorganometallic reactant.

In some embodiments the same metalorganic precursor is utilized in eachcycle. However, in other embodiments, different reactants can beutilized in one or more different cycles. In addition, the ALD processmay begin with any phase of the deposition cycle.

In one embodiment illustrated in FIG. 8, a vapor phase reactant pulsecomprising a Group IVB metal CHT reactant is provided to the reactionchamber where it contacts a substrate. Preferably the reactant isselected such that if it decomposes at the given process conditions itdoes not adversely affect the deposition process. Preferably the metalreactant comprises one or more of Ti, Hf, and Zr. In some embodiments,reactants are selected from the reactants of formula's (I), (II), (III),(IV), (V) and (VI).

Preferably, the metal CHT reactant is provided such that it forms nomore than about a single molecular layer on the substrate. If necessary,any excess metal reactant can be purged or removed from the reactionspace. In some embodiments, the purge step can comprise stopping theflow of metal reactant while still continuing the flow of an inertcarrier gas such as nitrogen or argon.

Next, a vapor phase reactant pulse comprising an oxygen source orprecursor is provided to the substrate and reaction chamber. Any of avariety of oxygen precursors can be used, including, without limitation:oxygen, plasma excited oxygen, atomic oxygen, ozone, water, nitric oxide(NO), nitrogen dioxide (NO₂), nitrous oxide (N₂O), hydrogen peroxide(H₂O₂), etc. A suitable oxygen precursor can be selected by the skilledartisan such that it reacts with the molecular layer of the metalreactant on the substrate to form a metal oxide under the particularprocess conditions. In some embodiments, ozone is used with a metal CHTreactant.

The oxygen source may be an oxygen-containing gas pulse and can be amixture of an oxygen precursor and inactive gas, such as nitrogen orargon. In some embodiments the oxygen source may be a molecularoxygen-containing gas pulse. One source of oxygen may be air. In someembodiments, the oxygen source or precursor is water. In someembodiments the oxygen source comprises an activated or excited oxygenspecies. In some embodiments the oxygen source comprises ozone. Theoxygen source may be pure ozone or a mixture of ozone and another gas,for example an inactive gas such as nitrogen or argon. In otherembodiments the oxygen source is oxygen plasma.

The oxygen precursor pulse may be provided, for example, by pulsingozone or a mixture of ozone and another gas into the reaction chamber.In other embodiments, ozone (or other oxygen precursor) is formed insidethe reactor, for example by conducting oxygen containing gas through anarc. In other embodiments an oxygen containing plasma is formed in thereactor. In some embodiments the plasma may be formed in situ on top ofthe substrate or in close proximity to the substrate. In otherembodiments the plasma is formed upstream of the reaction chamber in aremote plasma generator and plasma products are directed to the reactionchamber to contact the substrate. As will be appreciated by the skilledartisan, in the case of remote plasma the pathway to the substrate canbe optimized to maximize electrically neutral species and minimize ionsurvival before reaching the substrate.

Each metal oxide deposition cycle typically forms no more than about onemolecular layer of metal oxide. If necessary, any excess reactionbyproducts or oxygen precursor can be removed from the reaction space.In some embodiments, the purge step can comprise stopping the flow ofoxygen precursor while still continuing the flow of an inert carrier gassuch as nitrogen or argon. Preferably the oxygen precursor has adecomposition temperature above the substrate temperature duringdeposition. In some embodiments the oxygen precursor may decompose atthe substrate deposition temperature but does not disrupt the selflimiting nature of the ALD process.

The metal oxide deposition cycle is typically repeated a predeterminednumber of times 150 to form a metal oxide of the desired thickness andcomposition. In some embodiments, multiple molecular layers of metaloxide are formed by multiple deposition cycles. In other embodiments, amolecular layer or less of metal oxide is formed.

Removing excess reactants can include evacuating some of the contents ofthe reaction space or purging the reaction space with argon, helium,nitrogen or any other inert gas. In some embodiments purging cancomprise turning off the flow of the reactive gas while continuing toflow an inert carrier gas to the reaction space.

The precursors employed in the ALD type processes may be solid, liquidor gaseous material under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore it is conducted into the reaction chamber and contacted with thesubstrate surface. “Pulsing” a vaporized precursor onto the substratemeans that the precursor vapor is conducted into the chamber for alimited period of time. Typically, the pulsing time is from about 0.05to 10 seconds. However, depending on the substrate type and its surfacearea, the pulsing time may be even higher than 10 seconds. Preferably,for a 300 mm wafer in a single wafer ALD reactor, a metal precursor,such as a Ti, Hf, or Zr precursor, is pulsed for from 0.05 to 20seconds, more preferably for from 0.1 to 10 seconds and most preferablyfor about 0.3 to 5.0 seconds. An oxygen-containing precursor ispreferably pulsed for from about 0.05 to 10 seconds, more preferably forfrom 0.1 to 5 seconds, most preferably for from about 0.2 to 3.0seconds. However, pulsing times can be on the order of minutes in somecases, for example, if the process is applied to reactors having largesurface area, such batch ALD reactors. The optimum pulsing time can bereadily determined by the skilled artisan based on the particularcircumstances.

The mass flow rate of the precursors can also be determined by theskilled artisan. In one embodiment, for deposition on 300 mm wafers theflow rate of metal precursors is preferably between about 1 and 1000sccm without limitation, more preferably between about 100 and 500 sccm.The mass flow rate of the metal precursors is usually lower than themass flow rate of the oxygen source, which is usually between about 10and 10000 sccm without limitation, more preferably between about100-2000 sccm and most preferably between 100-1000 sccm.

The pressure in the reaction chamber is typically from about 0.01 toabout 20 mbar, more preferably from about 1 to about 10 mbar. However,in some cases the pressure will be higher or lower than this range, ascan be readily determined by the skilled artisan. Atmospheric pressurecould also be used for these high temperature reactions.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature. Growth temperatures aredescribed above and typically range from about 100 to about 400° C. Insome embodiments growth temperatures of greater than 300° C. or even350° C. are used.

The deposition cycles can be repeated a predetermined number of times oruntil a desired thickness is reached. Preferably, the thin films arebetween about 5 Å and 200 nm thick, more preferably between about 10 Åand 100 nm thick.

In other embodiments, transition metal nitride thin films are depositedusing a transition metal CHT reactant, preferably a Group IVB metal CHTreactant. The reaction conditions can be essentially as described abovefor deposition of transition metal oxide, except that anitrogen-containing reactant is used in place of the oxygen reactant.Nitrogen containing reactants may be, for example, NH₃, nitrogen plasma,N₂H₂, hydrogen azide, hydrazine and/or hydrazine derivatives, amines,nitrogen radicals, and other excited species of nitrogen.

In other embodiments, transition metal carbide thin films are depositedusing a transition metal CHT reactant, preferably a Group IVB metal CHTreactant. Again, the reaction conditions can be essentially as describedabove for deposition of transition metal oxides, except that acarbon-containing reactant is used in place of the oxygen reactant. Insome embodiments, the carbon source is a hydrocarbon such as an alkane,alkene, and/or alkyne.

Deposition of Thin Films Comprising Zirconium Oxide

In some embodiments, methods are provided for depositing thin filmscomprising zirconium oxide. A vapor phase pulse of a zirconium CHTprecursor is provided to the reaction chamber. The zirconium precursormay be selected from the group consisting of the compounds of formulas(I), (II), (III), (IV), (V) and (VI) above, where M is Zr. In someembodiments the precursor is (MeCp)ZrCHT. The zirconium precursor can beprovided such that it forms no more than one monolayer of material onthe substrate. Next, a vapor phase reactant pulse comprising an oxygenprecursor is provided to the reaction chamber. The oxygen precursor canbe provided such that it reacts with the zirconium precursor on thesubstrate surface. Preferred oxygen precursors include atomic oxygen,oxygen plasma, O₂, H₂O, O₃, NO, NO₂, N₂O, and H₂O₂. In some embodimentsthe oxygen precursor is O₃. Preferably the substrate temperature duringpulses of zirconium and oxygen precursors is above about 300° C. Thecycle can be generally referred to as a zirconium oxide depositioncycle. The deposition cycle can be repeated until the thin film reachesthe desired thickness.

The process conditions for the zirconium oxide deposition can beessentially as described above in reference to the metal oxidedeposition cycle.

Deposition of Thin Films Comprising Titanium Oxide

In some embodiments, methods are provided for depositing thin filmscomprising titanium oxide. A vapor phase pulse of a titanium CHTprecursor is provided to the reaction chamber. The titanium precursormay be selected from the group consisting of the compounds of formulas(I), (II), (III), (IV), (V) and (VI) above, where M is Ti. In someembodiments the precursor is CpTiCHT. The titanium precursor can beprovided such that it forms no more than one monolayer of material onthe substrate. Next, a vapor phase reactant pulse comprising an oxygenprecursor is provided to the reaction chamber. The oxygen precursor canbe provided such that it reacts with the titanium precursor on thesubstrate surface. Preferred oxygen precursors include atomic oxygen,oxygen plasma, O₂, H₂O, O₃, NO, NO₂, N₂O, and H₂O₂. In some embodimentsthe oxygen precursor is O₃. Preferably the substrate temperature duringpulses of titanium and oxygen precursors is above about 300° C. Thecycle can be generally referred to as a titanium oxide deposition cycle.The deposition cycle can be repeated until the thin film reaches thedesired thickness.

The process conditions for the titanium oxide deposition can beessentially as described above in reference to the metal oxidedeposition cycle.

Deposition of Thin Films Comprising Hafnium Oxide

In some embodiments, methods are provided for depositing thin filmscomprising hafnium oxide. A vapor phase pulse of a hafnium CHT precursoris provided to the reaction chamber. The hafnium precursor may beselected from the group consisting of the compounds of formulas (I),(II), (III), (IV), (V) and (VI) above, where M is Hf. The hafniumprecursor can be provided such that it forms no more than one monolayerof material on the substrate. Next, a vapor phase reactant pulsecomprising an oxygen precursor is provided to the reaction chamber. Theoxygen precursor can be provided such that it reacts with the hafniumprecursor on the substrate surface. Preferred oxygen precursors includeatomic oxygen, oxygen plasma, O_(2z) H₂O, O₃, NO, NO₂, N₂O, and H₂O₂. Insome embodiments the oxygen precursor is O₃. Preferably the substratetemperature during pulses of hafnium and oxygen precursors is aboveabout 300° C. The cycle can be generally referred to as a hafnium oxidedeposition cycle. The deposition cycle can be repeated until the thinfilm reaches the desired thickness.

The process conditions for the hafnium oxide deposition can beessentially as described above in reference to the metal oxidedeposition cycle.

Applications

Metal oxide films may be used, for example, as dielectric layers betweentop and bottom electrodes in capacitors. In some embodiments, acapacitor suitable for use in an integrated circuit is formed by amethod comprising:

depositing a bottom electrode;

depositing a dielectric oxide layer over the bottom electrode by anatomic layer deposition process comprising alternating and sequentialpulses of a metal CHT source and pulses of an oxygen source as describedherein; and

depositing a top electrode directly over and contacting the dielectriclayer.

The metal oxides can also be used as dielectric layers in transistors.In one embodiment of a method for forming a transistor in an integratedcircuit, a dielectric oxide layer is first deposited over one or moregate electrodes on a substrate by an ALD process. The deposition of thedielectric oxide layer can include any of the methods described herein.Preferably the dielectric oxide layer comprises one or more of hafnium,zirconium, and titanium. Next, a semiconductor is deposited on thedielectric oxide layer. In some embodiments the semiconductor comprisesone or more of silicon and germanium. Next, electrically conductivesource and drain electrodes are deposited on top of the semiconductorsuch that the drain electrodes align with the gate electrodes.

The skilled artisan will appreciate that the metal oxide thin filmsdescribed herein have many other uses, such as a floating gatedielectric layer in a flash device, as a blocking oxide in chargetrapping flash devices, as a gate dielectric in memory stacks, as adielectric oxide in other semiconductor devices, etc. The thin filmsdescribed herein can also be useful in optical areas, for example,titanium dioxide can be a transparent conducting oxide used in opticalcomponents, flat panel displays, LEDs, solar cells and chemical sensors.

Precursor Synthesis

Methods are also provided for synthesizing the metal CHT precursors usedin the ALD processes described herein. In particular, CHT precursors offormulas (I), (II), (III), (IV), (V) and (VI) above, can be synthesized.

In some embodiments the CHT precursor that is synthesized is CpTiCHT andin other embodiments the precursor (MeCp)ZrCHT is synthesized, asdescribed in the Examples below.

In other embodiments, transition metal precursors of formula (III) aresynthesized, such as (C₇H₈)M(C₇H₈), where M is a transition metal,preferably a group IVB metal such as Ti, Zr, Hf. In a containercontaining magnesium chips, anhydrous FeCl₃, cycloheptatriene, andtetrahydrofuran (THF) are combined. A transition metal precursor, suchas a transition metal halide THF adduct is added to the reactionmixture, preferably over a long period of time and while stirring. Thereaction is exothermic thus, for example, the transition metal precursormay be added over a 1-h period to avoid possible overheating of thestirred reaction mixture. The transition metal precursor comprises aGroup IVB metal in some embodiments, and may be, for example, atransition metal chloride. The transition metal precursor may be insolution, such as in solution with THF.

The mixture may be stirred over night, for example at room temperature.Following stirring, the volatile products may be evaporated undervacuum.

Synthesis of C₇H₈—Ti—C₇H₈ using TiCl₄ is described in Example 8 below.

EXAMPLES

All complex preparations were done under exclusion of air and moistureusing standard Schlenk and glove box techniques. Toluene and xylene weredried and stored over 4 Å molecular sieves. THF was freshly distilledfrom sodium benzophenone ketyl. Anhydrous Zirconium(IV) chloride(Aldrich 99.999%), Titanium(IV) chloride (Fluka >99.0%),Dicyclopentadienyl Titanium(IV) dichloride (Aldrich 97%), ferricchloride (Riedel-de Haen), magnesium turnings and cycloheptariene(Aldrich 90%) were used as received. Methylcyclopentadiene dimer wascracked to corresponding monomer just before usage.

¹H and ¹³C NMR spectra were recorded with a Varian Gemini 2000instrument at ambient temperature. Chemical shifts were referenced toSiMe₄ and are given in ppm. Thermogravimetric analyses were carried outon a Mettler Toledo Star^(e) system equipped with a TGA 850thermobalance using a flowing nitrogen atmosphere at 1 atm. The heatingrate was 10° C./min and the weights of the samples prepared to 70 μlpans were between 10-11 mg. Melting points were taken from the SDTA datameasured by the thermobalance. Mass spectra were recorded with a JEOLJMS-SX102 operating in electron impact mode (70 eV) using a directinsertion probe and sublimation temperature range of 50-370° C.

Example 1

Synthesis of (C₅H₅)Ti(C₇H₇): The synthesis was done using the method ofDemerseman et al. (Inorg. Chem. 1982, 21, 3942). CpTiCl₃ had to besynthesized initially and two different methods were employedsynthesizing different batches. First the method of Sloan at al. (J. Am.Chem. Soc. 1959, 81, 1364.) was employed. The method of Hitchcock et al.(Dalton Trans., 1999, 1161.) was also used as Cp₂TiCl₂ is readilyavailable.

In a 1-L flask containing 20 g of magnesium chips were added 2 g ofanhydrous FeCl₃, 50 ml of cycloheptatriene, 50 ml of THF, and, over a3-h period to allow the warming of the stirred reaction mixture, asolution of 57.45 g (0.26 mol) of CpTiCl₃ in 400 ml of THF. The mixturewas stirred at room temperature over night and the volatile productswere evaporated under vacuum. Sublimation of the residue (130° C./0.05mmHg) gave a blue solid: 85.8% yield (45.9 g); ¹H NMR (C₆D₆):), 4.91 (s,5H, CH), 5.43 (s, 7H, CH); ¹³C{¹H} NMR(C₆D₆): 97.35 (CH, C₇-ring), 86.71(CH, Cp ring); MS (EI, 70 eV) m/z: 204 (M⁺) with the correct isotopicdistribution.

FIG. 1 shows the structure of CpTiCHT and FIG. 2 provides the TGA curvemeasured for CpTiCHT.

Example 2

Synthesis of (MeC₅H₄)Zr(C₇H₇): The synthesis was performed in a fashionsimilar to that described for CpZrCHT by Tamm et al. (Organometallics2005, 3163). The method is also similar with that presented for CpTiCHTin Example 1 above. MeCpZrCl₃ needed in the synthesis was synthesizedusing the method of Hitchcock et al. (Polyhedron 1995, 14, 2745). ASchlenk flask was charged with magnesium turnings (6 g, 247 mmol),catalytic amounts of ferric chloride (0.6 g, 3.7 mmol), cycloheptatriene(15 ml), and THF (50 ml). This reaction mixture was treated dropwisewith a solution of MeCpZrCl₃ (17.3 g, 62.4 mmol) in THF (150 ml) over aperiod of 1 h. After the mixture was stirred overnight at roomtemperature, all volatiles were removed in vacuo. The air-sensitiveresidue was sublimed at 140° C./0.05 mbar to obtain 13.0 g (79.6%) of(MeC₅H₄)Zr(C₇H₇) as a purple crystalline solid. Anal. calcd. forZr₁C₁₃H₁₄: C, 33.65; H, 6.35. Found: C, 26.963; H, 5.03. Mp. 174-176°C., ¹H NMR (C₆D₆) 1.81 (s, 3H, CH₃), 5.14 (t, 2H, CH)), 5.23 (m, 2H, CH)5.24 (s, 7H, CH); ¹³C{¹H} NMR (C₆D₆) 14.61 (CH₃), 41.74 (Cp ring), 81.39(C₇-ring), 100.92 (Cp ring), 103.34 (Cp ring). MS (EI, 70 eV) m/z: 260(M⁺) with the correct isotopic distribution.

FIG. 1 shows the structure of (MeCp)ZrCHT and FIG. 2 provides the TGAcurve measured for this compound. (MeCp)ZrCHT is a solid precursor at100° C.

Example 3

The thermal stability of the CpTiCHT synthesized in Example 1 was testedon an extremely high surface area silica substrate and found to be good.The compound saturated the silica surface at 400° C., although theligands are most likely decomposed. CpTiCHT was observed to be a bluesolid that vaporized at 130° C.

Example 4

(MeCp)ZrCHT was synthesized as described above. (MeCp)ZrCHT was used incombination with O₃ in an ALD process essentially as described herein.An ozone concentration of 100 g/m³ was used. Smooth, uniform zirconiumoxide films were deposited at temperatures up to about 450° C.Saturation was confirmed at 350° C., and at 400° C. only slightdecomposition was observed as the growth rate increased from 0.7 Å/cyclewith 1 s pulses of the metal precursor to 0.8 Å/cycle with 2 s pulses.FIG. 3. According to ERDA, the films deposited at 350° C. wereexceptionally pure (no H detected, <0.06 at. % C). FIG. 4. XRD data ispresented in FIGS. 5 a, 5 b and 5c. GIXRD data is presented in FIG. 6.Similar characteristics were observed as with films deposited from(CpMe)₂Zr(OMe)Me and O₃.

Several of the deposited ZrO₂ films were tested for their electricalproperties. Preliminary results shown in FIG. 7 verify that the filmsact as dielectrics. A film deposited at 400° C. showed a CET of0.67-1.17 nm (6.2 nm/5.58 g/cm³).

Example 5

ZrO₂ is deposited by ALD from alternating pulses of (MeCp)ZrCHT oranother CHT metal precursor and an oxygen source, such as O₃ Thesubstrate temperature is above 300° C.

Example 6

HfO₂ is deposited on a substrate by ALD using alternating pulses of a HfCHT precursor and an oxygen source, such as O₃ at a substratetemperature of above 300° C.

Example 7

TiO₂ is deposited on a substrate by ALD using alternating pulses ofCpTiCHT and O₃ at a substrate temperature of above 300° C.

Example 8

Synthesis of CHT metal reactant: In a 1-L flask containing 5 g ofmagnesium chips were added 0.5 g of anhydrous FeCl₃, 30 ml ofcycloheptatriene, 30 ml of THF, and, over a 1-h period to allow thewarming of the stirred reaction mixture, a solution of 12 g (0.063 mol)of TiCl₄ in 200 ml of THF. The mixture was stirred at room temperatureover night, and the volatile products were evaporated under vacuum.Sublimation of the residue (130° C./0.05 mmHg) gave a dark solid: 24.4%yield (3.54 g); mp. 177-200° C.; ¹H NMR (C6D6): 1.2-1.5 (m, CH), 1.9-2.1(m, CH), 2.1-2.2 (m, CH), 4.2-4.4 (m, CH), 4.9-5.1 (CH, m), 5.32 (s, 7H,CH), 5.6-5.8 (m, CH); 13C{1H} NMR (C6D6): 37.34 (CH, C7-ring), 88.67(CH, η7-C7-ring), 101.53 (CH, C7-ring), 102.33 (CH, C7-ring), 113.39(CH, C7-ring); MS (EI, 70 eV) m/z: 278, 232, 230 [M]+, 91 [C7H7]+. Thechemical structure of the synthesized CHT compound was determined to be(C₇H₇)Ti(C₇H₉)/Ti(C₇H₈)₂. While this is believed to be accurate,identification of the structure was difficult and it was initiallyidentified differently. Crystal structure of the synthesized precursorsis shown in FIG. 9. TG, DTG and SDTA curves measured for (CHT)Ti(CHD)are shown in FIG. 10.

Other transition metals precursors of formula (III), such as(C₇H₇)M(C₇H₉)/M(C₇H₈)₂, where M is a transition metal, preferably groupIVB metal such as Ti, Zr, Hf, can be synthesized using essentially themethod described above for synthesis of (C₇H₇)Ti(C₇H₉)/M(C₇H₈)₂.

It will be appreciated by those skilled in the art that variousmodifications and changes can be made without departing from the scopeof the invention. Similar other modifications and changes are intendedto fall within the scope of the invention, as defined by the appendedclaims.

1. A method for forming a transition metal oxide thin film on asubstrate in a reaction chamber by atomic layer deposition, the methodcomprising: providing a vapor phase pulse of a first metalorganicreactant comprising a CHT ligand and a transition metal to the reactionchamber such that it forms no more than a monolayer on the substrate;removing excess first reactant from the reaction chamber; providing avapor phase pulse of a second reactant comprising oxygen to the reactionchamber; and removing excess second reactant and any reaction byproductsfrom the reaction chamber; wherein the providing and removing steps arerepeated until a thin metal oxide film of a desired thickness andcomposition is obtained, wherein the substrate temperature during theproviding and removing steps is above about 300° C.
 2. The method ofclaim 1, wherein the metalorganic reactant comprises a Group IVB metal.3. The method of claim 1, wherein the substrate temperature during theproviding and removing steps is above about 350° C.
 4. The method ofclaim 1, wherein the metalorganic reactant comprises one or more ofhafnium, titanium, and zirconium.
 5. The method of claim 1, wherein themetalorganic reactant is an organometallic reactant.
 6. The method ofclaim 1, wherein the metalorganic reactant comprises two ligands, one ofwhich is the cycloheptatrienyl (CHT, C₇H₇) ligand.
 7. The method ofclaim 6, wherein the metalorganic reactant comprises two CHT ligands. 8.The method of claim 6, wherein the metalorganic reactant comprises oneCHT ligand and one cyclopentadienyl (Cp) ligand.
 9. The method of claim6, wherein the metalorganic reactant does not comprise a halide.
 10. Themethod of claim 4, wherein the deposited thin film comprises ZrO₂. 11.The method of claim 4, wherein the deposited thin film comprises TiO₂.12. The method of claim 4, wherein the deposited thin film comprisesHfO₂.
 13. A method for forming a transition metal oxide thin film byatomic layer deposition on a substrate in a reaction chamber comprising:alternately and sequentially contacting the substrate with a vapor phasereactant pulse comprising a metal reactant and a vapor phase reactantpulse comprising an oxygen reactant, wherein the metal reactantcomprises a transition metal and two ligands, one of which is acycloheptatrienyl (CHT) ligand.
 14. The method of claim 13, wherein themetal reactant comprises a Group IVB metal.
 15. The method of claim 13,wherein the metal reactant is selected from reactants having the formula(I) R_(x)Cp-M-CHT, where RxCp represents substituted or unsubstitutedcyclopentadienyl, CHT is cycloheptatrienyl and M is selected from Ti, Zrand Hf.
 16. The method of claim 13, wherein the metal reactant isselected from reactants having the formula (II)(R₁R₂R₃R₄R₅R₆R₇)CHT-M-Cp(R₈R₉R₁₀R₁₁R₁₂), where M is selected from Ti, Zrand Hf, and R₁₋₁₂ can independently be H or an alkyl group.
 17. Themethod of claim 13, wherein the metal reactant is selected fromreactants having the formula (III)(R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHT(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄), where M is selected fromTi, Zr and Hf, and R₁₋₁₄ can independently be H or an alkyl group. 18.The method of claim 13, wherein the metal reactant is selected fromreactants having the formula (IV) R₁R₂R₃R₄R₅R₆R₇)CHT-M-L, where M isselected from Ti, Zr and Hf; R₁₋₇ can independently be H or an alkylgroup; and L is a mono or bidentate alkyl, cycloalkyl, alkoxy, amide orimido group or acyclic or cyclic dienyl ligand.
 19. The method of claim13, wherein the metal reactant is selected from reactants having theformula (V) R₁R₂R₃R₄R₅R₆R₇)CHT-M-CHD(R₈R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where Mis selected from Ti, Zr and Hf; R₁₋₁₆ can independently be H or an alkylgroup, and CHD is cyloheptadiene (C₇H₉).
 20. The method of claim 13,wherein the metal reactant is selected from reactants having the formula(VI) (R₁R₂R₃R₄R₅R₆R₇R₈)X-M-X(R₉R₁₀R₁₁R₁₂R₁₃R₁₄R₁₅R₁₆), where M isselected from Ti, Zr and Hf, R₁₋₁₄ can independently be H or an alkylgroup and X is cycloheptatriene (C₇H₈).
 21. The method of claim 13,wherein the oxygen reactant is selected from the group consisting of O₂,O₃, H₂O, NO, NO₂, N₂O, and H₂O₂.
 22. The method of claim 13, wherein thesubstrate temperature during the pulses is from about 100 to about 500°C.
 23. The method of claim 13, wherein the substrate temperature duringthe pulses is above about 300° C.
 24. The method of claim 13, whereinthe metal precursor comprises Ti.
 25. The method of claim 13, whereinthe metal precursor comprises Hf.
 26. The method of claim 13, whereinthe metal precursor comprises Zr.
 27. A method for forming a thin filmcomprising a transition metal by atomic layer deposition on a substratein a reaction space comprising: alternately and sequentially contactingthe substrate with a first vapor phase metal reactant pulse and a secondvapor phase reactant pulse; wherein the alternate and sequential pulsesare repeated until a thin film of a desired thickness and composition isobtained and wherein the metal reactant comprises a compound comprisinga transition metal and two cycloheptatriene (C₇H₈) ligands.
 28. Themethod of claim 27, wherein the metal reactant comprises a Group IVBmetal.
 29. The method of claim 28, wherein the metal reactant comprisesone of Ti, Hf and Zr.
 30. The method of claim 27, wherein the substratetemperature during the pulses is above about 300° C.
 31. The method ofclaim 27, wherein the thin film comprises a metal oxide.
 32. The methodof claim 31, wherein the second reactant is an oxygen source.
 33. Themethod of claim 32, wherein the second reactant comprises one or more ofO₂, H₂O, O₃, NO, NO₂, N₂O, and H₂O₂.
 34. The method of claim 27, whereinthe thin film comprises a metal nitride.
 35. The method of claim 34,wherein the second reactant is a nitrogen source.
 36. The method ofclaim 35, wherein the nitrogen source is selected from NH₃, N₂H₂, andnitrogen containing plasma.
 37. A method of synthesizing a CHT metalreactant comprising a transition metal, the method comprising forming areaction mixture by combining a transition metal reactant with ferricchloride, cycloheptatriene and tetrahydrofuran (THF) in a flaskcontaining magnesium chips.
 38. The method of claim 37, wherein thereaction mixture is stirred overnight.
 39. The method of claim 37,wherein the ferric chloride, cycloheptatriene and THF are first combinedand then the transition metal chloride is added.
 40. The method of claim39, wherein the transition metal chloride is added while warming themixture.
 41. The method of claim 39, wherein the transition metalreactant is a transition metal chloride.
 42. The method of claim 37,wherein the transition metal reactant is a Group IVB metal chloride. 43.The method of claim 37, wherein the Group IVB metal chloride is TiCl₄.44. The method of claim 37, wherein the CHT metal reactant comprises(C₇H₇)M(C₇H₉)/M(C₇H₈) (CHT-M-CHD).